"He may be a world-class narcissist, but this doesn’t make him mentally ill, because he does not suffer from the distress and impairment required to diagnose mental disorder."
That's from the Allen Frances letter. Now I realise I'm on dangerous ground, contradicting the psychiatrist who wrote the definition of narcissistic personality disorder, but I am slightly surprised to discover that you can only be deemed to be suffering from a mental disorder if you're distressed by it. What about psychopathy? Surely that is a notable example of a personality disorder that doesn't distress the people who exhibit it?
As for whether he's impaired by it, it strikes me that he is. If you, as leader of the free world, decide to have a meeting with another world leader on a matter of international security, and you hold that meeting in a resort where you can be overheard by other guests and waiting staff, doesn't that show that your decision-making is impaired? His impulsive behaviour, defensiveness, quickness to anger are all, to my mind, signs of impairment.